A particularly severe form of the pulmonary lymphatic disease lymphangioleiomyomatosis (LAM). Also works well in songs, due to it having the same number of syllables and the same beginning as the famous word in the Mary Poppins song.

When Elizabeth progressed from a little shortness of breath to needing a lung transplant in a month, she knew she had supercalymphangioleiomyomatosis.

"Supercalymphangioleiomyomatosis, even though the sound of it is something quite atrocious..."